Class FineDiffCopyOp

Persisted opcodes (string) are a sequence of atomic opcode. A single opcode
can be one of the following: c | c{n} | d | d{n} | i:{c} | i{length}:{s} 'c' =
copy one character from source 'c{n}' = copy n characters from source 'd' = skip
one character from source 'd{n}' = skip n characters from source 'i:{c} = insert
character 'c' 'i{n}:{s}' = insert string s, which is of length n

Do not exist as of now, under consideration: 'm{n}:{o} = move n characters
from source o characters ahead. It would be essentially a shortcut for a
delete->copy->insert command (swap) for when the inserted segment is
exactly the same as the deleted one, and with only a copy operation in between.
TODO: How often this case occurs? Is it worth it? Can only be done as a
postprocessing method (->optimize()?)